objtool: Trace instruction state changes during function validation

During function validation, objtool maintains a per-instruction state,
in particular to track call frame information. When tracing validation,
print any instruction state changes.

Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://patch.msgid.link/20251121095340.464045-12-alexandre.chartre@oracle.com

tools/objtool/check.c

@@ -3677,6 +3677,8 @@ static int validate_insn(struct objtool_file *file, struct symbol *func,
 			 struct instruction *prev_insn, struct instruction *next_insn,
 			 bool *dead_end)
 {
+	/* prev_state is not used if there is no disassembly support */
+	struct insn_state prev_state __maybe_unused;
 	struct alternative *alt;
 	u8 visited;
 	int ret;
@@ -3785,7 +3787,11 @@ static int validate_insn(struct objtool_file *file, struct symbol *func,
 	if (skip_alt_group(insn))
 		return 0;
 
-	if (handle_insn_ops(insn, next_insn, statep))
+	prev_state = *statep;
+	ret = handle_insn_ops(insn, next_insn, statep);
+	TRACE_INSN_STATE(insn, &prev_state, statep);
+
+	if (ret)
 		return 1;
 
 	switch (insn->type) {

tools/objtool/include/objtool/trace.h

@@ -30,6 +30,12 @@ extern int trace_depth;
 	}							\
 })
 
+#define TRACE_INSN_STATE(insn, sprev, snext)			\
+({								\
+	if (trace)						\
+		trace_insn_state(insn, sprev, snext);		\
+})
+
 static inline void trace_enable(void)
 {
 	trace = true;
@@ -53,10 +59,14 @@ static inline void trace_depth_dec(void)
 		trace_depth--;
 }
 
+void trace_insn_state(struct instruction *insn, struct insn_state *sprev,
+		      struct insn_state *snext);
+
 #else /* DISAS */
 
 #define TRACE(fmt, ...) ({})
 #define TRACE_INSN(insn, fmt, ...) ({})
+#define TRACE_INSN_STATE(insn, sprev, snext) ({})
 
 static inline void trace_enable(void) {}
 static inline void trace_disable(void) {}

tools/objtool/trace.c

@@ -7,3 +7,135 @@
 
 bool trace;
 int trace_depth;
+
+/*
+ * Macros to trace CFI state attributes changes.
+ */
+
+#define TRACE_CFI_ATTR(attr, prev, next, fmt, ...)		\
+({								\
+	if ((prev)->attr != (next)->attr)			\
+		TRACE("%s=" fmt " ", #attr, __VA_ARGS__);	\
+})
+
+#define TRACE_CFI_ATTR_BOOL(attr, prev, next)			\
+	TRACE_CFI_ATTR(attr, prev, next,			\
+		       "%s", (next)->attr ? "true" : "false")
+
+#define TRACE_CFI_ATTR_NUM(attr, prev, next, fmt)		\
+	TRACE_CFI_ATTR(attr, prev, next, fmt, (next)->attr)
+
+#define CFI_REG_NAME_MAXLEN   16
+
+/*
+ * Return the name of a register. Note that the same static buffer
+ * is returned if the name is dynamically generated.
+ */
+static const char *cfi_reg_name(unsigned int reg)
+{
+	static char rname_buffer[CFI_REG_NAME_MAXLEN];
+
+	switch (reg) {
+	case CFI_UNDEFINED:
+		return "<undefined>";
+	case CFI_CFA:
+		return "cfa";
+	case CFI_SP_INDIRECT:
+		return "(sp)";
+	case CFI_BP_INDIRECT:
+		return "(bp)";
+	}
+
+	if (snprintf(rname_buffer, CFI_REG_NAME_MAXLEN, "r%d", reg) == -1)
+		return "<error>";
+
+	return (const char *)rname_buffer;
+}
+
+/*
+ * Functions and macros to trace CFI registers changes.
+ */
+
+static void trace_cfi_reg(const char *prefix, int reg, const char *fmt,
+			  int base_prev, int offset_prev,
+			  int base_next, int offset_next)
+{
+	char *rname;
+
+	if (base_prev == base_next && offset_prev == offset_next)
+		return;
+
+	if (prefix)
+		TRACE("%s:", prefix);
+
+	if (base_next == CFI_UNDEFINED) {
+		TRACE("%1$s=<undef> ", cfi_reg_name(reg));
+	} else {
+		rname = strdup(cfi_reg_name(reg));
+		TRACE(fmt, rname, cfi_reg_name(base_next), offset_next);
+		free(rname);
+	}
+}
+
+static void trace_cfi_reg_val(const char *prefix, int reg,
+			      int base_prev, int offset_prev,
+			      int base_next, int offset_next)
+{
+	trace_cfi_reg(prefix, reg, "%1$s=%2$s%3$+d ",
+		      base_prev, offset_prev, base_next, offset_next);
+}
+
+static void trace_cfi_reg_ref(const char *prefix, int reg,
+			      int base_prev, int offset_prev,
+			      int base_next, int offset_next)
+{
+	trace_cfi_reg(prefix, reg, "%1$s=(%2$s%3$+d) ",
+		      base_prev, offset_prev, base_next, offset_next);
+}
+
+#define TRACE_CFI_REG_VAL(reg, prev, next)				\
+	trace_cfi_reg_val(NULL, reg, prev.base, prev.offset,		\
+			  next.base, next.offset)
+
+#define TRACE_CFI_REG_REF(reg, prev, next)				\
+	trace_cfi_reg_ref(NULL, reg, prev.base, prev.offset,		\
+			  next.base, next.offset)
+
+void trace_insn_state(struct instruction *insn, struct insn_state *sprev,
+		      struct insn_state *snext)
+{
+	struct cfi_state *cprev, *cnext;
+	int i;
+
+	if (!memcmp(sprev, snext, sizeof(struct insn_state)))
+		return;
+
+	cprev = &sprev->cfi;
+	cnext = &snext->cfi;
+
+	disas_print_insn(stderr, objtool_disas_ctx, insn,
+			 trace_depth - 1, "state: ");
+
+	/* print registers changes */
+	TRACE_CFI_REG_VAL(CFI_CFA, cprev->cfa, cnext->cfa);
+	for (i = 0; i < CFI_NUM_REGS; i++) {
+		TRACE_CFI_REG_VAL(i, cprev->vals[i], cnext->vals[i]);
+		TRACE_CFI_REG_REF(i, cprev->regs[i], cnext->regs[i]);
+	}
+
+	/* print attributes changes */
+	TRACE_CFI_ATTR_NUM(stack_size, cprev, cnext, "%d");
+	TRACE_CFI_ATTR_BOOL(drap, cprev, cnext);
+	if (cnext->drap) {
+		trace_cfi_reg_val("drap", cnext->drap_reg,
+				  cprev->drap_reg, cprev->drap_offset,
+				  cnext->drap_reg, cnext->drap_offset);
+	}
+	TRACE_CFI_ATTR_BOOL(bp_scratch, cprev, cnext);
+	TRACE_CFI_ATTR_NUM(instr, sprev, snext, "%d");
+	TRACE_CFI_ATTR_NUM(uaccess_stack, sprev, snext, "%u");
+
+	TRACE("\n");
+
+	insn->trace = 1;
+}